In fuel management systems for internal combustion engines, on-board computers are currently supplied with data from sensors monitoring various engine operating parameters, such as RPM, temperature, exhaust gas characteristics, mass air flow through the air intake manifold, accelerator pedal position, etc., to determine the proper fuel-air ratio for fuel economy, smoothness of engine operations and compliance with emission standards. The electrical control signals are supplied to a solenoid controlled fuel injection valve which typically is biased closed by a spring so that a large electrical current is required to open the valve. In this example, while modern electronic computers and microprocessors have been developed to provide highly accurate control signals for controlling liquid flow, the control devices per se have typically been a solenoid controlled mechanical valve which have difficulty in accurately tracking electrical signals and delivering short liquid pulses mainly because of their large pintle mass which is magnified in the case of springs biasing them closed. The leading edge in particular of the liquid pulse delivered to the utilization system is not sharp. In the case of solenoid controlled fuel injectors for internal combustion engines, the output nozzles are very sensitive to fluid loading so that if a passageway to direct the output fuel pulse to a specific port intake target were attached, the performance is severely degraded. Reference is made to the article entitled "Electronic Fuel Injection" by Randolph, October 1984, Popular Science, pages 73-75; Automotive Engineering, October 1983, pages 40-45 and the phamplet "High Technology from Buick", "the 3.8 SF Turbo".
Significant improvements in such systems have been provided in the above-identified related application of R. D. Stouffer wherein a bistable fluidic switch element with a cross-over type interaction chamber leading to a common outlet and to a pair of output passageways, one of the output passageways leading to the engine and the other leading to the supply tank. The bistable switch was reliably switched using a pair of control ports which had control tubes coupled thereto and shaken in prescribed manner by a solenoid which, in turn, was controlled by the on-board computer or microprocessor. In the Stouffer system, individual fuel return from each injectior provides for "flushing" of fuel vapor bubbles which might enter the fuel inlet. The conventional system described earlier herein (and described more fully hereafter) has no means for flushing out a vapor bubble once it has entered the inlet. This feature allows the bistable fluidic switch system to use a lower system fuel pressure (on the high pressure rail). Current systems (such as those marketed by Robert Bosch) use approximately 27 to 37 psi to avoid the formation of vapor bubbles. Lower pressure systems require less complexity and less expensive pump.
An object of the present invention is to provide an improved fuel injection system of the type disclosed in the above-referenced Stouffer application. A further object of the invention is to provide improvements in fuel injection systems generally, particularly with respect to method and apparatus for improving the engine performance thereof.
According to one major feature of the invention, a switch pin is projected into and out of intrusion position in the flow path of fluid in the power nozzle of the fluidic element to cause switching in the chamber of the bistable switch. In other words, the use of side channels or control ports is eliminated and the fuel switching is accomplished solely by the interposition of a pin in the power nozzle thus simplifying the construction of the fluidic itself, eliminating small flow passages and the like and, at the same time, improving the response time, since there is no flow of fluid inside channels or delay involved in such flow. In a preferred embodiment, the axis of the power nozzle is canted relative to the axis of the chamber of the fluidic element so that in the absence of the pin, the switch is in one predetermined state and is switched form that state to the other state by pin intrusion and always returns to that predetermined state on removal of the intrusion pin.
A second major feature of the invention is that air is supplied to each injector at a point in the output flow passage leading to the engine so as to pre-air atomize the fuel before injection of same into the air intake manifold on the engine. This has the following advantages:
A. It makes the flow calibration insensitive to changes in manifold vacuum--thereby eliminating the need to compensate the supply pressure for changes in manifold vacuum.
B. It improves the quality of the fuel/air spray which is of primary importance in fuel/air mixture preparation. Improved spray (smaller droplets) and distribution in the air stream flowing in the air intake manifold results in a greater degree of fuel vaporization, yielding more complete combustion. The improvements is manifested by smoother engine idle and substantial minimization of "idle shake".
C. For improved cold/warm-up operation, air supplied to the injectors may be selectively preheated, to improve early fuel vaporization characteristics. This technique is more effective than heating 100 percent of the combustion air during the first few minutes after a cold start (when very little heat is available). Thus, improved warm-up exhaust emissions will result.
D. Air supplied directly to the injectors is accounted for by the engine control computer. When the air flow is computed based on the manifold absolute pressure, the injector air is accounted for by its effect on manifold pressure. In a fuel metering system which makes use of direct air mass flow measurement, the source of injector air is downstream of the mass flow sensor. In either case, the source of injector air is derived from a source downstream of the combustion air filter.
E. The injector air flows in proportion to the manifold vacuum (atmospheric pressure minus manifold absolute pressure), producing the best spray (smallest droplet size) under idle and light load conditions, when the vacuum is high--(15-20 in.hg.) and coincidentally, the engine combustion is most sensitive to droplet size at idle and light load conditions.
F. Finally, the pin has a low mass. The low mass electromechanical actuator allows the injector to turn on and off with less delay than conventional injectors. This results in a flow calibration which maintains its linearity at pulse widths below 2 msec.
G. The introduction of air isolates the high vacuum condition of the engine from the fluidic element. Air enters the engine output leg of the fluidic element so that particular point does not see the vacuum of the intake manifold. There is not enough air added to greatly effect engine vacuum. The power nozzle then becomes the major source of pressure drop of the fluid in the system.
In the preferred embodiment, both major features are utilized but it will be appreciated that either feature can be used independently of the other and still obtain advantages of the invention.
Thus, the basic objective of the invention is to provide an improved fuel injection system for internal combustion engines. A further object of the invention is to provide an improved bistable fluidic switch which has no control ports or passages; and a further object of the invention is to provide an improved fuel preparation by the addition of filtered and monitored air to fuel for internal combustion engines prior to induction in the engine.